A bioinspired molybdenum–copper molecular catalyst for CO(2) electroreduction

Non-noble metal molecular catalysts mediating the electrocatalytic reduction of carbon dioxide are still scarce. This work reports the electrochemical reduction of CO(2) to formate catalyzed by the bimetallic complex [(bdt)Mo(VI)(O)S(2)Cu(I)CN](2–) (bdt = benzenedithiolate), a mimic of the active site of the Mo–Cu carbon monoxide dehydrogenase enzyme (CODH2). Infrared spectroelectrochemical (IR-SEC) studies coupled with density functional theory (DFT) computations revealed that the complex is only a pre-catalyst, the active catalyst being generated upon reduction in the presence of CO(2). We found that the two-electron reduction of [(bdt)Mo(VI)(O)S(2)Cu(I)CN](2–) triggers the transfer of the oxo moiety to CO(2) forming CO(3)(2–) and the complex [(bdt)Mo(IV)S(2)Cu(I)CN](2–) and that a further one-electron reduction is needed to generate the active catalyst. Its protonation yields a reactive Mo(V)H hydride intermediate which reacts with CO(2) to produce formate. These findings are particularly relevant to the design of catalysts from metal oxo precursors.